<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .container {
            width: 1200px;
            margin: 0 auto;
        }
        .nav {
            height: 50px;
            background-color: darkcyan;
        }
        .main {
            height: 800px;
            background-color: darkseagreen;
        }
        .footer {
            height: 100px;
            background-color: darkviolet;
        }
    </style>
</head>
<body>
<div class="container">
    <div class="nav"></div>
    <div class="main"></div>
    <div class="footer"></div>
</div>
</body>
</html>